/Engine/Source/Runtime/Slate/Public/Framework/Application/SlateApplication.h
HACK: Don't use this unless shutting down a game viewport Game viewport windows need to be destroyed instantly or else the viewport could tick and access deleted data
void DestroyWindowImmediately ( [TSharedRef](API\Runtime\Core\Templates\TSharedRef)< [SWindow](API\Runtime\SlateCore\Widgets\SWindow) > WindowToDestroy )